Remove instances of schema.ConfigModeAttr

[rileykarson]

ConfigMode: schema.ConfigModeAttr is a setting that enables Attributes as blocks mode (https://www.terraform.io/language/attr-as-blocks) in Terraform, which corrected a breakage in Terraform Core between 0.11 and 0.12. It allows empty blocks to be specified, which is important to allow unsetting certain fields. However, it can result in negative behaviour for modules and advanced configurations, so we should try and remove occurrences of the setting.

This likely means attempting to correct O+C fields or similar. We've never scoped what removing this looks like.

[c2thorn]

Noting that schema.ConfigModeAttr affected #18115

[c2thorn]

closed with GoogleCloudPlatform/magic-modules#11506

[github-actions]

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